In-vehicle human body detecting method

ABSTRACT

Chest motion associated with breathing is detected to obtain a breathing motion signal representing the chest motion in the form of an electrical signal; then, the times at which specific points occur in the waveform of the breathing motion signal are detected and, when the time interval between the specific points is within a predetermined range, the presence of a human body is detected in a vehicle.

TECHNICAL FIELD

The present invention relates to a method for detecting the presence ofa human body and, more particularly, to a method for detecting thepresence of a human body in a vehicle.

BACKGROUND ART

It is practiced to detect the movement of a person inside a vehicle byusing a radar sensor, an ultrasonic sensor, or the like. For example,Tokuhyouhei (Published Japanese translation of PCT application) No.8-507706 (WO 94/20021) discloses an invention concerning an ultrasonicmotion monitor for monitoring the breathing motions of a human being orother mammals. Further, Japanese Unexamined Patent Publication No.7-204166 and Japanese Patent No. 2827534 disclose that the presence of ahuman body is detected by detecting the breathing motions of a human byusing a piezoelectric element.

There often occur such accidents as a child being left in a vehicle inthe intense heat of summer and dying, because of the heat, in thevehicle. To prevent the occurrence of such a tragedy, a system is beingstudied that detects the presence of a human inside a vehicle, and thatissues some kind of alarm when the temperature inside the vehiclebecomes excessively high.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to detect the presence of ahuman body such as an infant inside a vehicle by using a breathingmotion signal.

According to the present invention, chest motion associated withbreathing is detected to obtain a breathing motion signal representingthe chest motion in the form of an electrical signal; then, based on thewaveform of this signal, it is determined whether or not the detectedmotion is a human breathing motion and, if it is a human breathingmotion, the presence of a human body is detected in the vehicle.

More specifically, the times at which specific points occur in thewaveform of the breathing motion signal are detected and, when the timeinterval between the specific points is within a predetermined range,the presence of a human body is detected in the vehicle.

Here, provisions are made to avoid the occurrence of false detection dueto noise introduced into the signal by external disturbances.

According to a first embodiment of the present invention, the times(T(n)) at which peaks occur on the positive or negative side of thewaveform of the breathing motion signal are detected to obtain apeak-to-peak time interval (ΔT(n)), a difference (Δt(n)) betweenpeak-to-peak time intervals is obtained from the peak-to-peak timeinterval (ΔT(n)), the number of times that the difference (Δt(n))between the peak-to-peak time intervals is smaller than a predeterminedvalue (Tth) is counted by a counter, and when the number of timescounted is larger than a predetermined number (Cth), the presence of ahuman body is detected in the vehicle.

According to a second embodiment of the present invention, the times(Tu(n)) at which the waveform of the breathing motion signal rises orfalls are detected to obtain a time interval (ΔTu(n)) between the risingor falling times, a difference (Δtu(n)) between time intervals isobtained from the time interval (ΔTu(n)), the number of times that thedifference (Δtu(n)) between the time intervals is smaller than apredetermined value (Tuth) is counted by a counter, and when the numberof times counted is larger than the predetermined number (Cth), thepresence of a human body is detected in the vehicle.

According to a third embodiment of the present invention, a waveformwidth time interval (ΔTud(n)) of the breathing motion signal isdetected, a difference (Δtud(n)) between waveform width time intervalsis obtained from the waveform width time interval (ΔTud(n)), the numberof times that the difference (Δtud(n)) between the waveform width timeintervals is smaller than a predetermined value (Tudth) is counted by acounter, and when the number of times counted is larger than thepredetermined number (Cth), the presence of a human body is detected inthe vehicle.

According to a fourth embodiment of the present invention, the times atwhich positive and negative peaks occur in the waveform of the breathingmotion signal are detected, the ratio of the time interval from thepositive peak to the negative peak or from the negative peak to thepositive peak to the time interval from the positive peak to the nextpositive peak is obtained, the number of times that the ratio is withina predetermined range is counted by a counter, and when the number oftimes counted is larger than the predetermined number (Cth), thepresence of a human body is detected in the vehicle.

According to the present invention, the difference (Δt(n)) between thepeak-to-peak intervals on the waveform of the breathing motion signal isobtained, and the presence of a human body is detected based on thatdifference. Accordingly, it can be correctly determined whether thedetected motion is a human breathing motion or not, irrespective ofvariations in breathing cycle among people.

Further, the number of times that the difference (Δt(n)) between thepeak-to-peak time intervals is smaller than the predetermined value(Tth) is counted by the counter and, when the number of times counted islarger than the predetermined number (Cth), it is determined that thedetected motion is a human breathing motion, and the presence of a humanbody is thus detected. This ensures reliable detection of the presenceof a human body.

When the peaks are not larger in magnitude than a predetermined level(Vth1), the counter is reset, thereby avoiding the occurrence of faultdetection due to external disturbances or other factors than breathingmotion.

According to the present invention, the difference (Δtud(n)) between thewidth time intervals on the waveform of the breathing motion signal isobtained, and the presence of a human body is detected based on thatdifference. Accordingly, it can be correctly determined whether thedetected motion is a human breathing motion or not, irrespective ofvariations in breathing cycle among people.

According to the present invention, the times at which positive andnegative peaks occur in the waveform of the breathing motion signal aredetected, the ratio of the time interval from the positive peak to thenegative peak or from the negative peak to the positive peak to the timeinterval from the positive peak to the next positive peak is obtained,and the presence of a human body is detected based on that ratio.Accordingly, it can be correctly determined whether the detected motionis a human breathing motion or not, irrespective of variations inbreathing cycle among people.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing one example of a human body detectionapparatus for implementing a method for detecting a human body in avehicle according to the present invention.

FIG. 2 is a diagram showing the signal waveform of a human breathingmotion obtained by the human body detection apparatus.

FIG. 3 is a diagram showing in flowchart form a human body detectionmethod according to the present invention.

FIG. 4 is a diagram showing in flowchart form a human body detectionmethod according to the present invention.

FIG. 5 is a modification of the flowchart shown in FIG. 4.

FIG. 6 is a diagram for explaining a human body detection methodaccording to the present invention, in which the presence of a humanbody is detected when two conditions are satisfied.

FIG. 7 is a diagram for explaining a human body detection methodaccording to the present invention, in which the presence of a humanbody is detected when two conditions are satisfied.

FIG. 8 is a diagram for explaining a human body detection methodaccording to the present invention, in which the presence of a humanbody is detected when two conditions are satisfied.

FIG. 9 is a diagram for explaining a human body detection methodaccording to the present invention, in which the presence of a humanbody is detected when a plurality of conditions are satisfied.

FIG. 10 is a diagram showing in flowchart form a human body detectionmethod according to the present invention.

FIG. 11 is a diagram showing the signal waveform of a human breathingmotion obtained by the human body detection apparatus.

FIG. 12 is a diagram showing in flowchart form a human body detectionmethod according to the present invention.

FIG. 13 is a diagram showing the signal waveform of a human breathingmotion obtained by the human body detection apparatus.

FIG. 14 is a diagram showing in flowchart form a human body detectionmethod according to the present invention.

FIG. 15 is a diagram showing the signal waveform of a human breathingmotion obtained by the human body detection apparatus.

FIG. 16 is a diagram showing in flowchart form a human body detectionmethod according to the present invention.

FIG. 17 is a diagram for explaining a human body detection methodaccording to the present invention, in which the presence of a humanbody is detected when two conditions are satisfied.

FIG. 18 is a diagram for explaining a human body detection methodaccording to the present invention, in which the presence of a humanbody is detected when two conditions are satisfied.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a diagram showing one example of a human body detectionapparatus for implementing a method for detecting a human body in avehicle according to the present invention. Reference numeral 1 is asensor section which includes an oscillator 11, a transmitter 12, atransmitting antenna TA, a receiving antenna RA, a receiver 13, and amixer 14. An output of the oscillator 11 is fed to the transmitter 12and radiated from the transmitting antenna TA toward a human body. Thereflected wave from the chest of the breathing human body is received bythe receiving antenna RA, and the received reflected wave is fed fromthe receiver 13 into the mixer 14 where the output of the receiver 13 ismixed with a portion of the output of the oscillator 11. The signalproduced by mixing is fed to a filtering section 2, and a breathingmotion signal Sbr output from it is fed to an A/D converter 3 andprocessed in a signal processing section 4 to detect the presence of thehuman body. The output of the signal processing section 4 is supplied toan alarm device 5 which, if required, issues an alarm when the presenceof the human body is detected by the signal processing section 4.

The configuration of the sensor section of the human body detectionapparatus described above is only one example of the configuration forobtaining the breathing motion signal waveform, and other sensors suchas an ultrasonic sensor or a piezoelectric element can be used to obtainthe breathing motion signal.

According to the present invention, the breathing motion signal isprocessed and, when a prescribed condition or conditions are satisfied,it is determined that the presence of a human body has been detected.The breathing motion signal is processed by the signal processingcircuit 4 shown in FIG. 1, and detections, calculations, decisions, etc.described in the flowcharts illustrating the embodiments herein areperformed in the signal processing section.

Embodiment 1

FIG. 2 is a diagram showing the signal waveform of a human's breathingmotion obtained by the human body detection apparatus. In the case ofthe human body detection apparatus of FIG. 1, this signal waveform isthe waveform of the output signal of the filtering section 2. Theabscissa represents the time (seconds), and the ordinate represents thebreathing motion expressed in volts (V).

According to the first embodiment, the times at which peaks occur in thesignal waveform shown in FIG. 2 are detected, and the time intervalbetween each peak is calculated. Since, usually, a human breathingmotion is substantially periodic, the difference Δt between any twosuccessive peak-to-peak time intervals ΔT is normally substantiallyconstant. Therefore, in the present invention, when the difference Δtbetween the peak-to-peak time intervals ΔT is smaller than apredetermined value, it is determined that the detected motion is ahuman breathing motion.

FIG. 3 is a diagram showing, in flowchart form, a human body detectionmethod according to the present invention. In FIG. 3, first the timesT(n) at which peaks occur in the breathing motion waveform are detected(S1). Next, the peak-to-peak time interval ΔT(n)=T(n)−T(n−1) iscalculated (S2). Then, the difference Δt(n) between peak-to-peak timeintervals ΔT(n) is calculated (S3). The difference Δt(n) between thepeak-to-peak time intervals is the difference between ΔT(n) and ΔT(n−1),which is calculated asΔt(n)=|ΔT(n)−ΔT(n−1)| (absolute value)whereΔT=T(n)−T(n−1) andΔT(n−1)=T(n−1)−T(n−2)Normally, the period of human breathing is substantially constant, andthe difference Δt(n) between the peak-to-peak time intervals isextremely small. Accordingly, if this difference is smaller than apredetermined value, it can be determined that the detected motion is ahuman breathing motion.

Therefore, it is next determined whether Δt(n) is smaller than thepredetermined threshold value Tth (S4) and, if the conditionΔt(n)<Tthis satisfied (Yes), then it is determined that the waveform represents ahuman's breathing motion, thus detecting the presence of a human body(S5). If No in S4, the process is terminated thereupon.

In the above embodiment, the presence of a human body is detected bydetecting the times at which peaks occur on the positive side of thesignal waveform, but the presence of a human body can also be detectedby detecting the times at which peaks (bottoms) occur on the negativeside of the signal waveform.

FIG. 4 is a diagram showing in flowchart form another human bodydetection method according to the present invention. In the flowchartshown in FIG. 3, when it is detected that Δt(n)<Tth, it is determinedthat the waveform represents a human breathing motion, and the presenceof a human body is thus detected. On the other hand, in the flowchartshown in FIG. 4, when the condition Δt(n)<Tth has been detected morethan a predetermined number of times, it is determined that the waveformrepresents a human breathing motion, thus detecting the presence of ahuman body.

In FIG. 4, S1 to S4 are the same as the corresponding steps in the flowof FIG. 3. If the conditionΔt(n)<Tthis satisfied in S4 (Yes), counter value CT is incremented by 1, i.e.,CT=CTn+1 (S5). On the other hand, if the conditionΔt(n)<Tthis not satisfied in S4 (No), the counter value CT is reset, i.e., CT=0(S6). Next, it is determined whether CT is larger than the predeterminednumber Cth (S7) and, if the conditionCT>Cthis satisfied (Yes), it is determined that the waveform represents ahuman breathing motion, and the presence of a human body is thusdetected (S8); if the answer is No, the process is terminated thereupon.

FIG. 5 is a modification of the flowchart shown in FIG. 4. Thedifference from FIG. 4 is that S4-1 is inserted after S4. In FIG. 5, ifit is determined thatΔt(n)<Tthin S4 (Yes), then it is determined whether the peak level V(n) of thebreathing motion signal waveform shown in FIG. 2 is larger than apredetermined level Vth1 (see FIG. 2) (S4-1). If the conditionV(n)>Vth1is satisfied (Yes), the counter value CT is incremented by 1, i.e.,CT=CTn+1 (S5). On the other hand, if the conditionV(n)>Vth1is not satisfied in S₄-1 (No), the counter value CT is reset, i.e., CT=0(S6). The reason that the counter is reset here is that if the peaklevel V(n) of the breathing motion signal waveform is smaller than thepredetermined level Vth1 (No in S4-1), there is the possibility that thedetected waveform may not be that of a breathing motion but may merelybe that of noise.

Next, it is determined whether CT is larger than the predeterminednumber Cth (S7) and, if the conditionCT>Cthis satisfied (Yes), it is determined that the waveform represents ahuman breathing motion, thus detecting the presence of a human body(S8).

In this way, by incrementing the counter value only when the signallevel is larger than the predetermined value (Vth1), noise due toexternal disturbance can be eliminated from the target of detection.

FIG. 6 is a diagram illustrating a human body detection method accordingto the present invention by using an AND circuit. In the flowchart ofFIG. 3, if it is determined in S4 that Δt(n)<Tth (Yes), and if the peaklevel V(n) of the breathing motion signal waveform is larger than apredetermined level Vth2 that is larger than Vth1 (V(n)>Vth2), then itis determined that the presence of a human body has been detected. Thatis, when the condition Δt(n)<Tth and the condition V(n)>Vth2 are bothsatisfied, the AND circuit produces an output, thus detecting thepresence of a human body. Here, the condition is set that the signallevel is larger than the predetermined level Vth2 that is larger thanthe level Vth1, in order to ensure that the detection is made only whenthe breathing motion signal occurs.

As described above, Vth2 is set larger than Vth1. The values of Vth1 andVth2 shown in FIG. 2 are only examples, and can be changed as needed.

FIG. 7 shows a method in which, in the flowchart of FIG. 4, if it isdetermined in S7 that CT>Cth (Yes), and if the peak level V(n) of thebreathing motion signal waveform is larger than the predetermined levelVth2 (V(n)>Vth2), then it is determined that the presence of a humanbody has been detected. That is, when the condition CT>Cth and thecondition V(n)>Vth2 are both satisfied, the AND circuit produces anoutput, thus detecting the presence of a human body.

FIG. 8 shows a method in which, in the flowchart of FIG. 5, if thesignal peak level is larger than Vth1 in S4-1, therefore not causing thecounter value to be reset, and if it is determined in S7 that CT>Cth(Yes), then if the peak level V(n) of the breathing motion signalwaveform is larger than the predetermined level Vth2 (V(n)>Vth2), it isdetermined that the presence of a human body has been detected. That is,when the signal peak level V(n) is larger than the predetermined levelVth1, therefore not causing the counter value to be reset, and when thecondition CT>Cth and the condition V(n)>Vth2 are both satisfied, the ANDcircuit produces an output, thus detecting the presence of a human body.

The difference from FIG. 7 is that since CT>Cth, the condition V(n)>Vth1is satisfied.

FIG. 9 is a diagram illustrating a method for detecting the presence ofa human body by combining the following conditions described withreference to the flowcharts of FIGS. 3 to 5.

Conditions

-   -   (1) Δt(n)<Tth    -   (2) V(n)>Vth1    -   (3) V(n)>Vth2

Since a human breathing motion is a cyclic repetition of inhaling andexhaling, one followed by the other, the signal waveform of thebreathing motion swings positive and negative alternately as shown inFIG. 2. The upper half of FIG. 9 shows a method for detecting thepresence of a human body based on the peaks on the positive side of thebreathing motion signal waveform shown in FIG. 2, while the lower halfshows a method for detecting the presence of a human body based on thepeaks on the negative side of the signal waveform. The human bodydetection method will be described below with reference to FIG. 9.

First, from the detected times of the peaks on the positive side of thewaveform, it is determined whether Δt(n)<Tth (Sp1), and then, from thepeak level on the positive side of the waveform, it is determinedwhether V(n)>Vth1 (Sp2). When these two conditions are satisfied, an ANDcircuit (Sp3) produces an output, which is counted by a counter, andwhen the counter counts up to a predetermined number (Sp4), the value isheld (Sp5). In this embodiment, the reason that the value is held hereis that if the value is not held, two outputs (Sp4 and Sp7) to an ANDcircuit (Sp9) may be shifted in timing and displaced from each other andthe AND circuit may not produce an output. When the value is held (Sp5),one of the conditions for the AND circuit (Sp9) holds. On the otherhand, from the peak level on the positive side of the waveform, it isdetermined whether V(n)>Vth2 (Sp6); if the answer is Yes, the event iscounted by a counter, and when the counter counts up to a predeterminednumber (Sp7), the value is held. When the value is held (Sp8), the otherone of the conditions for the AND circuit (Sp9) holds. When the twoconditions for the AND circuit hold, its output is held (Sp10), and oneof the conditions for an AND circuit (S11) thus holds.

Next, from the detected times of the peaks on the negative side of thewaveform, it is determined whether Δt(n)<Tth (Sm1), and then, from thepeak level on the negative side of the waveform, it is determinedwhether V(n)>Vth1 (Sm2). When these two conditions are satisfied, an ANDcircuit (Sm3) produces an output, which is counted by a counter, andwhen the counter counts up to a predetermined number (Sm4), the value isheld. When the value is held (Sm5), one of the conditions for an ANDcircuit (Sm9) holds. On the other hand, from the amplitude of thewaveform on the negative side, it is determined whether V(n)>Vth2 (Sm6);if the answer is Yes, the event is counted by a counter, and when thecounter counts up to a predetermined number (Sm7), the value is held.When the value is held (Sm8), the other one of the conditions for theAND circuit (Sm9) holds. When the two conditions for the AND circuithold, its output is held, and the other one of the conditions for theAND circuit (S11) thus holds. When the two conditions for the ANDcircuit hold, it is determined that the presence of a human body hasbeen detected.

In the above example, the presence of a human body is detected only whenthe two conditions hold for the AND circuit (S11), but alternatively,the presence of a human body may be detected when either one of the ANDcircuits (Sp9 or Sm9) has produced an output. In the above example,Δt(n) and V(n) are both absolute values.

FIG. 10 is a diagram showing in flowchart form a human body detectionmethod according to the present invention; in this method, when thepeak-to-peak time interval has been within a predetermined time intervalrange over a predetermined number of times, then it is determined thatthe signal represents a human breathing motion, and the presence of ahuman body is thus detected.

In FIG. 10, first the times T(n) at which peaks occur in the breathingmotion signal are detected (S1). Next, the peak-to-peak time intervalΔT(n)=T(n)−T(n−1) is calculated (S2). Then, it is determined whether thepeak-to-peak time interval ΔT(n) is within the predetermined timeinterval range (S3). For example, when the lower limit of thepredetermined time interval range is denoted by Ttha and the upper limitby Tthb, then if the conditionTtha<ΔT(n)<Tthbis satisfied (Yes), the counter value CT is incremented by 1, i.e.,CT=CTn+1 (S4). On the other hand, if the conditionTtha<ΔT(n)<Tthbis not satisfied in S3 (No), the counter value CT is reset, i.e., CT=0(S5). Next, it is determined whether CT is larger than the predeterminednumber Cth (S6) and, if the conditionCT>Cthis satisfied (Yes), it is determined that the waveform represents ahuman breathing motion, and the presence of a human body is thusdetected (S7).

Embodiment 2

While, in the first embodiment, the human body detection has beenperformed by detecting the times at which peaks occur in the breathingmotion signal waveform, in a second embodiment the presence of a humanbody is detected by detecting the times at which the breathing motionsignal waveform rises (or falls).

FIG. 11 is a diagram similar to FIG. 2, showing the signal waveform of ahuman breathing motion. The abscissa represents the time (seconds), andthe ordinate represents the breathing motion detected and expressed involts (V). The difference from FIG. 2 is that the times Tu(n) at whichthe signal waveform rises are detected.

FIG. 12 is a diagram showing in flowchart form the human detectionmethod according to the second embodiment. In FIG. 12, the times Tu(n)at which the signal waveform rises are detected (S1). Next, therise-to-rise time interval ΔTu(n)=Tu(n)−Tu(n−1) is calculated (S2).Then, the difference Δtu(n) between rise-to-rise time intervals iscalculated (S3). The difference Δtu(n) between the rise-to-rise timeintervals is the difference between the time intervals ΔTu(n), which iscalculated asΔtu(n)=|ΔTu(n)−ΔTu(n−1)| (absolute value)whereΔTu(n)=Tu(n)−Tu(n−1) andΔTu(n−1)=Tu(n−1)−Tu(n−2)

Next, it is determined whether Δtu(n) is smaller than a predeterminedthreshold value Tuth (S4). If the conditionΔtu(n)<Tuthis satisfied (Yes), the counter value CT is incremented by 1, i.e.,CT=CTn+1 (S5). On the other hand, if the conditionΔtu(n)<Tuthis not satisfied in S4 (No), the counter value CT is reset, i.e., CT=0(S6). Next, it is determined whether CT is larger than the predeterminednumber Cth (S7) and, if the conditionCT>Cthis satisfied (Yes), it is determined that the waveform represents ahuman breathing motion, and the presence of a human body is thusdetected (S8).

In the above flowchart, the times Tu(n), at which the signal rises, havebeen detected but, alternatively, the times Td(n) at which the signalfalls may be detected. In the above description, the waveform on thepositive side of the signal has been used, but instead, the waveform onthe negative side may be used.

Embodiment 3

The human body detection has been performed in the first embodiment bydetecting the times at which peaks occur in the breathing motion signalwaveform, and in the second embodiment by detecting the times at whichthe breathing motion signal waveform rises (or falls); in contrast, in athird embodiment, the presence of a human body is detected by detectingthe time width of the breathing motion signal waveform (the timeinterval between the rising and falling of the waveform).

FIG. 13 is a diagram similar to FIG. 2, showing the signal waveform of ahuman breathing motion. The abscissa represents the time (seconds), andthe ordinate represents the breathing motion detected and expressed involts (V). The difference from FIG. 2 is that the time width ΔTud(n) ofthe signal waveform is detected.

FIG. 14 is a diagram showing in flowchart form the human detectionmethod according to the third embodiment. In FIG. 14, the time Tu(n) atwhich the signal waveform rises is detected (S1). Next, the time Td(n)at which the signal waveform falls is detected (S2). Then, the timeinterval (hereinafter referred to as the “signal waveform width”)ΔTud(n) between the time Tu(n) at which the signal waveform rises andthe time Td(n) at which the signal waveform falls is calculated asfollows (S3).ΔTud(n)=Td(n)−Tu(n)

After obtaining each signal waveform width as described above, thedifference Δtud(n) between signal waveform widths is obtained as follows(S4).Δtud(n)=|ΔTud(n)−ΔTud(n−1)|Then, it is determined whether Δtud(n) is smaller than a predeterminedvalue Tudth (S6). If the conditionΔtud(n)<Tudthis satisfied (Yes), the counter value CT is incremented by 1, i.e.,CT=CTn+1 (S6). On the other hand, if the conditionΔtud(n)<Tudthis not satisfied in S5 (No), the counter value CT is reset, i.e., CT=0(S7). Next, it is determined whether CT is larger than the predeterminednumber Cth (SB) and, if the conditionCT>Cthis satisfied (Yes), it is determined that the waveform represents ahuman breathing motion, and the presence of a human body is thusdetected (S9).

Embodiment 4

While, in the first embodiment, the human body detection has beenperformed by detecting the times at which peaks occur in the breathingmotion signal waveform, in a fourth embodiment the times at whichpositive and negative peaks occur in the breathing motion signalwaveform are detected, and the time interval from the positive peak tothe negative peak and the time interval from the negative peak to thepositive peak are calculated; then, the ratio of the time interval fromthe positive peak to the negative peak to the time interval from thepositive peak to the next positive peak is calculated, and the presenceof a human body is detected based on this ratio.

FIG. 15 is a diagram similar to FIG. 2, showing the signal waveform of ahuman breathing motion. The abscissa represents the time (seconds), andthe ordinate represents the breathing motion detected and expressed involts (V). The difference from FIG. 2 is that the times at whichpositive and negative peaks occur in the signal waveform are detected.

FIG. 16 is a diagram showing in flowchart form the human detectionmethod according to the fourth embodiment. In FIG. 16, peak time Tp(n)on the positive side of the signal waveform is detected (S1), and peak(bottom) time Tb(n) on the negative side is detected (S2). Next, thetime interval ΔTpb(n) from the positive peak to the negative peak andthe time interval ΔTbp(n) from the negative peak to the positive peakare calculated as follows (S2).ΔTpb(n)=Tb(n)−Tp(n)ΔTbp(n)=Tp(n)−Tb(n)Next, the ratio of the time interval from the positive peak to thenegative peak to the time interval from the positive peak to the nextpositive peak is calculated as follows (S4).ΔTα(n)=ΔTpb(n)/(ΔTpb(n)+ΔTbp(n))

Then, it is determined whether ΔTα(n) is within a prescribed range, inaccordance with the following condition (S5). Tαl<ΔTα(n)<Tαh (Tαl is thelower limit value of the ratio, and Tαh is the upper limit value of theratio)

If Yes is determined in S5, the counter value CT is incremented by 1,i.e., CT=CTn+1 (S6). On the other hand, if No is determined in S5, thecounter value CT is reset, i.e., CT=0 (S7). Next, it is determinedwhether CT is larger than the predetermined number Cth (S8) and, if theconditionCT>Cthis satisfied (Yes), it is determined that the waveform represents ahuman breathing motion, and the presence of a human body is thusdetected (S9).

In the above example, the ratio of the time interval from the positivepeak to the negative peak to the time interval between the positivepeaks has been obtained, but instead, the ratio of the time intervalfrom the negative peak to the positive peak to the time interval betweenthe positive peaks may be obtained. Alternatively, the ratio of the timeinterval from the positive peak to the negative peak or the timeinterval from the negative peak to the positive peak to the timeinterval between the negative peaks may be obtained.

FIG. 17 shows a method in which, if it is determined that Δt(n)<Tth(Yes) in S4 in the flowchart of FIG. 3, and if the ratio ΔTα(n) in FIG.16 satisfies the condition Tαl<ΔTα(n)<Tαh, then it is determined thatthe presence of a human body has been detected. That is, when thecondition Δt(n)<Tth and the condition Tαl<ΔTα(n)<Tαh are both satisfied,the AND circuit produces an output, thus detecting the presence of ahuman body.

FIG. 18 shows a method in which if it is determined that CT<Cth (Yes) inS7 in the flowchart of FIG. 4, and if the ratio ΔTα(n) in FIG. 16satisfies the condition Tαl<ΔTα(n)<Tαh, then it is determined that thepresence of a human body has been detected. That is, when the conditionΔt(n)<Tth and the condition Tαl<ΔTα(n)<Tαh are both satisfied, the ANDcircuit produces an output, thus detecting the presence of a human body.

1. A human body detection method for detecting a human body in avehicle, comprising: detecting chest motion associated with breathingand obtaining a breathing motion signal representing said chest motionin the form of an electrical signal; detecting times at which specificpoints occur in a waveform of said breathing motion signal; anddetecting the presence of a human body in said vehicle when timeinterval between said specific points is within a predetermined range.2. A human body detection method as claimed in claim 1, wherein saidspecific points in the waveform of said breathing motion signal arepeaks on a positive or negative side of the waveform of said breathingmotion signal, and wherein the times (T(n)) at which said peaks occurare detected to obtain a peak-to-peak time interval (ΔT(n)), adifference (Δt(n)) between peak-to-peak time intervals is obtained fromsaid peak-to-peak time interval (ΔT(n)), and the presence of a humanbody is detected in said vehicle when the difference (Δt(n)) betweensaid peak-to-peak time intervals is smaller than a predetermined value(Tth).
 3. A human body detection method as claimed in claim 2, whereinthe number of times that the difference (Δt(n)) between saidpeak-to-peak time intervals is smaller than said predetermined value(Tth) is counted by a counter and, when the number of times counted islarger than a predetermined number (Cth), the presence of a human bodyis detected in said vehicle.
 4. A human body detection method as claimedin claim 3, wherein said counter is reset when said peaks are not largerin magnitude than a predetermined level (Vth1).
 5. A human bodydetection method as claimed in claim 2 wherein, when the difference(Δt(n)) between said peak-to-peak time intervals is smaller than saidpredetermined value (Tth), and when said peaks are larger in magnitudethan a predetermined level (Vth2), the presence of a human body isdetected in said vehicle.
 6. A human body detection method as claimed inclaim 3 wherein, when the number of times counted is larger than saidpredetermined number (Cth), and when said peaks are larger in magnitudethan a predetermined level (Vth2), the presence of a human body isdetected in said vehicle.
 7. A human body detection method as claimed inclaim 4 wherein, when said counter is not reset, and the number of timescounted is larger than said predetermined number (Cth), and when saidpeaks are larger in magnitude than a predetermined level (Vth2), thepresence of a human body is detected in said vehicle.
 8. A human bodydetection method as claimed in claim 2 wherein, when two conditions, onebeing that the difference (Δt(n)) between said peak-to-peak timeintervals is smaller than said predetermined value (Tth) and the otherbeing that said peaks are larger in magnitude than a predetermined level(Vth1), are satisfied (CONDITION 1), and when the condition that saidpeaks are larger in magnitude than a predetermined level (Vth2) issatisfied (CONDITION 2), the presence of a human body is detected insaid vehicle.
 9. A human body detection method as claimed in claim 2wherein, when two conditions, one being that the difference (Δt(n))between said peak-to-peak time intervals is smaller than saidpredetermined value (Tth) and the other being that said peaks are largerin magnitude than a predetermined level (Vth1), are satisfied on boththe positive and negative sides of said waveform (CONDITION 1), and whenthe condition that said peaks are larger in magnitude than apredetermined level (Vth2) is satisfied (CONDITION 2), the presence of ahuman body is detected in said vehicle.
 10. A human body detectionmethod as claimed in claim 8 wherein, when said CONDITION 1 and saidCONDITION 2 are respectively satisfied a predetermined number of times,outputs thereof are held, and an AND circuit produces an output todetect the presence of a human body in said vehicle.
 11. A human bodydetection method as claimed in claim 9 wherein, when said CONDITION 1and said CONDITION 2 are respectively satisfied a predetermined numberof times, outputs thereof are held, and AND circuits produces outputs,which are held and are input to an AND circuit that follows said ANDcircuits, and when conditions for said AND circuit are satisfied on bothsaid positive and negative sides, the presence of a human body isdetected in said vehicle.
 12. A human body detection method as claimedin claim 2 wherein, when said peak-to-peak time interval (ΔT(n)) iswithin a predetermined time interval range, the presence of a human bodyis detected in said vehicle.
 13. A human body detection method asclaimed in claim 1, wherein said specific points in the waveform of saidbreathing motion signal are rising or falling points of the waveform ofsaid breathing motion signal, and wherein the times (Tu(n)) at whichsaid rising or falling points occur are detected to obtain a timeinterval (ΔTu(n)) between said rising or falling points, a difference(Δtu(n)) between time intervals is obtained from said time interval(ΔTu(n)), the number of times that the difference (Δtu(n)) between saidtime intervals is smaller than a predetermined value (Tuth) is countedby a counter, and when the number of times counted is larger than apredetermined number (Cth), the presence of a human body is detected insaid vehicle.
 14. A human body detection method as claimed in claim 1,wherein said specific points in the waveform of said breathing motionsignal are points defining a waveform width of said breathing motionsignal, and wherein time interval (ΔTud(n)) of said waveform width isdetected, a difference (Δtud(n)) between waveform width time intervalsis obtained from said waveform width time interval (ΔTud(n)), the numberof times that the difference (Δtud(n)) between said waveform width timeintervals is smaller than a predetermined value (Tudth) is counted by acounter, and when the number of times counted is larger than apredetermined number (Cth), the presence of a human body is detected insaid vehicle.
 15. A human body detection method as claimed in claim 1,wherein said specific points in the waveform of said breathing motionsignal are positive and negative peaks of the waveform of said breathingmotion signal, and wherein the times at which said positive and negativepeaks occur are detected, the ratio of the time interval from saidpositive peak to said negative peak or from said negative peak to saidpositive peak to the time interval from said positive peak to the nextpositive peak is obtained, the number of times that said ratio is withina predetermined range is counted by a counter, and when the number oftimes counted is larger than a predetermined number (Cth), the presenceof a human body is detected in said vehicle.
 16. A human body detectionmethod as claimed in claim 15, wherein the ratio of the time intervalfrom said positive peak to said negative peak or from said negative peakto said positive peak to the time interval from said negative peak tothe next negative peak is obtained, the number of times that said ratiois within said predetermined range is counted by said counter, and whenthe number of times counted is larger than said predetermined number(Cth), the presence of a human body is detected in said vehicle.
 17. Ahuman body detection method as claimed in claim 15 wherein, when thenumber of times that said ratio is within said predetermined range,counted by said counter, is larger than said predetermined number (Cth),and when the difference (Δt(n)) between said peak-to-peak time intervalsin the waveform of said breathing motion signal is smaller than apredetermined value (Tth), the presence of a human body is detected insaid vehicle.
 18. A human body detection method as claimed in claim 15wherein, when the number of times that said ratio is within saidpredetermined range, counted by said counter, is larger than saidpredetermined number (Cth), and when the number of times that thedifference (Δt(n)) between said peak-to-peak time intervals in thewaveform of said breathing motion signal is smaller than saidpredetermined value (Tth), counted by said counter, is larger than saidpredetermined number (Cth), the presence of a human body is detected insaid vehicle.
 19. A human body detection apparatus comprising: means fordetecting chest motion associated with breathing and obtaining abreathing motion signal representing said chest motion in the form of anelectrical signal; means for detecting times at which specific pointsoccur in a waveform of said breathing motion signal; and means fordetecting the presence of a human body in a vehicle when time intervalbetween said specific points is within a predetermined range.
 20. Avehicle providing a human body detection apparatus comprising: means fordetecting chest motion associated with breathing and obtaining abreathing motion signal representing said chest motion in the form of anelectrical signal; means for detecting times at which specific pointsoccur in a waveform of said breathing motion signal; and means fordetecting the presence of a human body in a vehicle when time intervalbetween said specific points is within a predetermined range.